Currently, it is difficult to implement single-fiber bi-directional receiving and transmitting of light of the same wavelength, that is, to separate a receiving optical path and a transmitting optical path from each other for the light of the same wavelength by using the same fiber. As shown in FIG. 1, in the prior art, a filter transmits a part of light and reflects apart of light, and therefore, the light in a direction is transmitted directly through the filter, and the light in another direction is reflected at the filter, thereby changing the optical path and separating the receiving optical path and the transmitting optical path from each other for the light of the same wavelength by using the same fiber.
However, with the filter that transmits a part of light and reflects a part of light, the transmit optical power and the receiver sensitivity of the optical subassembly are impaired.